XI THE SPECIAL COLOURS OF PLANTS 323 



modification, become quite self-fertile. This is the case with 

 the garden-pea, and also with our beautiful bee-orchis, in which 

 the pollen-masses constantly fall on to the stigmas, and the 

 flower, being thus self-fertilised, produces abundance of capsules 

 and of seed. Yet in many of its close allies insect agency is 

 absolutely required ; but in one of these, the fly-orchis, com- 

 paratively very little seed is produced, and self -fertilisation 

 would therefore be advantageous to it. When garden-peas 

 were artificially cross-fertilised by Mr. Darwin, it seemed to do 

 them no good, as the seeds from these crosses produced less 

 vigorous plants than seed from those which were self-fertilised ; 

 a fact directly opposed to what usually occurs in cross-fer- 

 tilised plants. 



5. As oj^posed to the theory that there is any absolute need 

 for cross-fertilisation, it has been urged by Mr. Henslow and 

 others that many self- fertilised plants are exceptionally vigorous, 

 such as groundsel, chick weed, sow-thistle, buttercups, and other 

 common weeds ; while most plants of world-Avide distribution 

 are self-fertilised, and these have proved themselves to be best 

 fitted to survive in the battle of life. More than fifty species 

 of common British plants are very widely distributed, and all 

 are habitually self -fertilised.^ That self -fertilisation has some 

 great advantage is shown by the fact that it is usually the 

 species which have the smallest and least conspicuous flowers 

 which have spread ^videly, while the large and showy flowered 

 species of the same genera or families, which require insects to 

 cross-fertilise them, have a much more limited distribution. 



6. It is now believed by some botanists that many in- 

 conspicuous and imperfect flowers, including those that are 

 Avind-fertilised, such as plantains, nettles, sedges, and grasses, 

 do not represent primitive or undeveloped forms, but are 

 degradations from more perfect flowers which were once 

 adapted to insect fertilisation. In almost every order we find 

 some plants which have become thus reduced or degraded for 

 ^Wnd or self-fertilisation, as Poterium and Sanguisorba among 

 the Rosacese ; while this has certainly been the case in the 

 cleistogamic flowers. In most of the above-mentioned plants 

 there are distinct rudiments of petals or other floral organs, 



^ Henslow's " Self-Fertilisation," Trans. Linn. Soc, Second series, Botany, 

 vol. i. p. 391. 



